Help needed understanding a MOSFET chart

Thread Starter

Xelectro

Joined Aug 12, 2012
1
Hi
I am currently experimenting with a power MOSFET IRF510
And I am trying to understand how to properly read the output characteristic chart, to determine required Vth to bias the MOSFET drain at half rail voltage (class A amp).
Vcc 12v
Rload 24R
Id (max) 500ma
Desired id at bussing 250ma
Need help understanding the chart.
Thanks
 

crutschow

Joined Mar 14, 2008
24,397
Because of the large unit-to-unit variation of Vth you can't use that by itself to bias the transistor at 1/2 the supply voltage. Thus a resistor is typically added between the transistor source and ground to swamp out the Vth variations and give a more stable bias point. Since this resistor also reduces the transistor gain you can bypass it with a capacitor to increase the gain for AC signals. Here is a discussion of biasing.
 
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